1. Field of the Invention
The present invention relates to a seat lifter and, more particularly, to a seat lifter for vehicle seats.
2. Description of the Prior Art
A conventional seat lifter, as shown in FIG. 1, includes two pairs of links 2,3 and each pair of links 2,3 is respectively disposed at a front and a rear portion of a side of a seat (not shown). An end of each of the links 2,3 is pivoted on a lower bracket 1 which is to be mounted on a vehicle body (not shown) with a pivot pin 10,11 and the other end of each of the links 2,3 is pivoted on an upper bracket 4 supporting a seat cushion (not shown) of the seat.
One of the links 2, which is positioned along the side of the front of the seat, is operatively connected to a clutch means such as a spring coupler apparatus 6 through a plate 8. One end of the plate 8 is pivoted on the link 2 and the other end of the plate 8 is pivoted on a driven member of the clutch means 6. The clutch means 6 has a lever 7; and by manually operating the lever 7, the driven member 6 is rotated. However, the rotation of the driven member 6 will not be transmitted to the lever 7. Thus, in accordance with the manual rotation of the lever 7, the position of the driven member 6 is changed and the driven member 6 is arrested at the changed position.
Therefore, as shown in FIG. 1, the link 2 is rotated around the pin 10 through the plate 8 in a direction shown by an arrow (C), since the end of the plate 8 is rotated in a direction shown by an arrow (B) in response to rotation of the lever 7 in a direction shown by an arrow (A). As each link 2,3 is connected to each other through the upper bracket 4, the upper bracket 4 for the seat cushion is lifted upwards as an entire unit. Thus, the height of the seat cushion is adjusted.
Accordingly, with such a vehicle seat, the position of the seat cushion may be raised on occasions where an occupant in the seat is short and the position of the seat cushion may be lowered on occasions where the occupant in the seat is tall. As a result, every occupant may select an optimal position for driving the vehicle comfortably.
However, in the above conventional seat lifter, the links 2,3 are arranged approximately parallel to each other; and the size of the links 2,3 is substantially equal to each other. Thus, as shown in FIG. 1a, the upper bracket 4 for the seat cushion is lifted as a unit. By raising the height of the seat cushion, a front end of the seat cushion which supports the knee portion of the occupant is also raised; so that if the occupant is short and the legs of the occupant are also short, the feet of the occupant may not reach adequately the vehicle floor. Thus, it will be hard to operate a braking pedal, an acceleration pedal, or a clutch pedal provided on the vehicle floor.
Further, a bracket 9 for a seat back (not shown) is provided on the upper bracket 4. Thus, the relative position between the seat cushion and the seat back, or the length of the seat cushion, is not changed by adjusting the height of the seat cushion, even though the femoral length of the seat is varied.
Besides, since the seat cushion is mounted on the upper bracket 4, the upper bracket 4 must have enough thickness; and the structure thereof must be sufficient to withstand a heavy load on the seat cushion. Further, the clutch means is connected to the link 2 which is positioned at the front side so as to easily operate the lever. Therefore, the front links 2 are readily arrested. However, the rear links 3, substantially supporting the waist of the occupant, are arrested through the upper bracket 4. As the rear portion of the upper bracket 4 will easily rattle, the rear links 3 need adequate mechanical strength.
Still further, in the event that the spring coupler apparatus is used as the clutch means, a play of the driven member 6 thereof cannot be avoided. Accordingly, since the link 2 connected to the driven member oscillates, it can be uncomfortable to sit on the seat cushion.